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As the green building industry has evolved, so has the way concrete helps structures become more sustainable. Concrete can help earn points toward LEED certification in every major credit category. And as LEED-NC has evolved, the way it treats concrete has, too.

One of the most striking changes is in the Materials & Resources category, says David Shepherd, director of sustainable development for PCA. “As green becomes more mainstream, what we did five years ago becomes more readily accepted as standard operating procedure,” he explains. Because USGBC’s mission is to transform the marketplace, he says, they raise the bar: where in earlier versions of LEED-NC a building could earn one point toward Credit 4.1 for using 5 percent recycled content, that has now doubled to requiring 10 percent recycled content, and the same goes for Credit 4.2 — doubled to requiring 20 percent recycled content.

“That revision touts the impact of concrete,” explains Shepherd. “They’re changing how concrete is specified, and giving more value to that part of concrete that has the biggest impact…and encouraging use of supplementary cementitious materials.”

Energy efficiency: E2 City Homes

One of the surest ways to earn points for energy efficiency in both residential and commercial construction is by using concrete in the building envelope. The Urban Project put this idea to use in its E2 City Homes development in Minneapolis. The two-story, four-unit residential complex used insulating concrete forms (ICFs) from Reward Wall Systems and was a LEED-H pilot project, earning Gold certification — and numerous awards.

ICFs are stay-in-place forms made of foam, into which reinforcing steel and concrete are placed to create a sandwich wall with a high R-value, extreme durability and strength, sound-dampening qualities, insect resistance and fire safety. In the case of the E2 City Homes, ICFs helped the homes earn a low HERS rating, a measure of energy efficiency that impacts how a home earns points toward LEED certification.

Donn Thompson, PCA’s program manager for residential technology, explains: If a home has a HERS rating of 100, it meets the minimum requirements of the model energy code — a prerequisite for LEED-H EA Credit 1.1. Each point reduction in a HERS rating refers to a 1 percent improvement in energy consumption above the prerequisite; the E2 City Homes had impressive HERS ratings ranging between 50 and 54.

The E2 City Homes development in Minneapolis used ICFs to earn low HERS ratings, which contributed to earning more points toward their eventual Gold certification in LEED-H. Photo by Dana Wheelock, courtesy of LHB.

Durability

Concrete is built to last. Many concrete building systems can withstand the raw forces of wind, flood or fire. Because concrete structures are so solid and long lasting, their shells can often be maintained in reconstruction projects — earning points in the Materials and Resources category for Building Reuse Credits 1.1 and 1.2.

The use of supplementary cementitious materials like slag cement and fly ash is growing every year, and in many cases these materials serve to strengthen concrete mixes and increase their structural resistance to sulfate attack or alkali-silica reactions, and to help them perform better in freeze-thaw conditions. These qualities help buildings become more durable than ever — and the incorporation of recycled materials earns even more points toward LEED credits.

The North Central College Res/Rec Center’s precast concrete components include recycled slag aggregate in the mix. Image courtesy of Dukane Precast, Inc.

Thinking locally: North Central College Res/Rec Center

In Naperville, Ill., students at North Central College are looking forward to the fall 2009 opening of a new fieldhouse with an indoor track, a 100,000-square-foot recreation center and four field courts — a much-needed resource improvement for a school with a track program with 47 national championships under its belt. Wrapped around the facility is a dorm for 350 students, a space-saving design that takes advantage of local land resources in the downtown area.

Dukane Precast’s double-wall precast concrete components for walls and floors help the structure conserve resources, says the company’s vice president of sales and marketing, Brian Bock. (A bonus: the use of recycled slag aggregate from a local plant makes the concrete both lighter and stronger.) The form-finished sandwich-like components are filled with high R-value bio-based foam, and the resulting interior walls need only a coat of paint to become warm and inviting for students — while minimizing energy demands. The facility will also use geothermal wells and radiant floor heating.

Bock says energy, performance and aesthetics drove the decision to create a unified facility. “The efficiency of heating one building instead of two is huge,” he says, and because the exterior walls are made with a brick form liner and painted to look like the real thing, the building blends with surrounding downtown structures. Bock and his team hope for LEED Gold certification.

The E2 City Homes development in Minneapolis shatter outmoded stereotypes of what a concrete home is like; the interiors are warm, comfortable and inviting — and award-winning, with accolades from the National Association of Home Builders and Insulating Concrete Form Association, among others. Photo by Dana Wheelock, courtesy of LHB.

Indoor air quality

One of the strongest concerns for sustainability-savvy building tenants and consumers is VOC emissions, and here, concrete does an admirable job of reducing VOCs. Compared to concrete, acrylic latex paint, plywood paneling and water-based EVA wall and floor glue release and emit significantly higher amounts of VOCs. Employing exposed concrete surfaces (which can be stained and stamped to produce limitless colors and patterns) cuts VOCs immensely.

Plus, concrete more than three inches thick acts as an air barrier, reducing moisture infiltration (and the chance for mold development) and helping owners better control — and typically reduce — their HVAC needs.

Resource Efficiency: Great River Energy Headquarters

The recently finished Great River Energy headquarters in Maple Grove, Minn., “Will be the most energy-efficient office building ever constructed in Minnesota and one of the most energy-efficient in the world,” says CEO David Saggau. Architects Perkins + Will and general contractor McGough Construction have designed and constructed a poured-in-place concrete structure that contains fly ash replacement of between 40 percent and 50 percent.

In line with the company’s goal to make best use of natural resources, the building will harvest daylight through multiple light-filled atriums; a two-way post-tensioned flat plate gravity load system does this by using floor plates made up of four long, narrow “pods” with either atrium or exterior spaces between them. The shallowest system available, it allows the project to use raised floors throughout to accommodate mechanical air distribution, and to have high ceilings and shallow floor-to-floor heights to maximize daylight penetration. The company is aiming for LEED Platinum certification.

Sidebar: Reducing the Urban Heat Island effect

One of the ways pervious concrete pavement (any concrete pavement, in fact) can help earn LEED points and have an otherwise positive impact is by reducing the urban heat island (UHI) effect. A heat island is a local area of elevated temperature in a region of cooler temperatures; heat islands occur where there is a preponderance of dark exterior building materials and pavements, and a lack of vegetation.

Research performed by CTL Group in 2007 evaluated the reflective properties of concrete, using the LEED NC SS Credit 7.1 Heat Island Effect: Non-Roof criteria, and found that 45 different concrete samples tested — regardless of the mix (some of which included recovered materials like fly ash and slag cement) — met the required criteria.